FILE - Protesters march in Chicago before a rally with Republican presidential candidate Donald Trump at the University of Illinois-Chicago, March 11, 2016. Trump's strong language throughout his campaign has drawn in some supporters perceived as hate-filled extremists.

The Anti-Defamation League in the U.S. said Wednesday that thousands of anti-Semitic hate messages targeted Jewish journalists in the last year after many of them wrote articles that were perceived as even mildly critical of Republican presidential candidate Donald Trump.

The group, which monitors ethnic slurs and bigotry against Jews, said that 19,253 anti-Semitic Twitter comments were sent to 800 reporters between August 2015 and July. It covered the period when Trump took command of the Republican presidential nominating contest while besting 16 other candidates to become the party's standard bearer in next month's election against Democrat Hillary Clinton.

A Trump campaign spokeswoman, Hope Hicks said in a statement to the New York Times in response to the report that “We have no knowledge of this activity and strongly condemn any commentary that is anti-Semitic.”

The Anti-Defamation League said the anti-Semitic comments came from 1,600 Twitter accounts and that the senders were "disproportionately likely to identify as Donald Trump supporters, conservatives, or part of the ‘alt-right,’ a loosely connected group of extremists, some of whom are white supremacists." The group said it was not implying that the Trump campaign supported or endorsed the anti-Semitic tweets, "only that certain self-styled supporters sent these ugly messages."

The ADL said that 10 journalists, all Jews, bore the brunt of the anti-Semitic attacks, receiving 83 percent of the comments on their Twitter accounts. The list of targeted journalists included conservative columnist Ben Shapiro, Tablet's Yair Rosenberg, Atlantic magazine's Jeffrey Goldberg, The New York Times' Jonathan Weisman and CNN's Jake Tapper. Some non-Jewish journalists were also targeted because they were perceived to be Jewish, the group said.

The ADL said the comments were likely "connected to the anti-Semitic tropes related to Jews ‘controlling’ the media, and the media ‘controlling’ the government."

Jonathan Greenblatt, ADL's chief executive, said, "The spike in hate we've seen online this election cycle is extremely troubling and unlike anything we have seen in modern politics. A half century ago, the [Ku Klux Klan] burned crosses. Today, extremists are burning up Twitter."